1. Field of the Invention
This invention relates to polymer-modified asphalt compositions. More particularly, this inventions relates to polymer-modified asphalt compositions prepared from asphalt, a glycidyl-containing ethylene copolymer and a block copolymer derived from styrene and a conjugated-diene.
2. Description of the Related Art
It is well known that polymers can be used to modify the rheological properties of asphalt. A wide variety of polymers have been used for this purpose and numerous polymer-modified asphalt compositions are known in the art.
For example, polymer-modified asphalt compositions prepared using styrene/conjugated-diene block copolymers are described in "Modification of Asphalt by Block Polymers of Butadiene and Styrene" by G. Kraus, Rubber Chemistry and Technology, Vol. 55, No. 5, November-December 1982. Polymer-modified asphalts are also discussed in "Asphalt and Polymer Modified Asphalt Properties Related to the Performance of Asphalt Concrete Mixes" by J. L. Goodrich, Proc. of the Association of Asphalt Paving Technologists, Vol. 52, pp. 116-160 (1988).
Additionally, U.S. Pat. No. 4,217,259, issued Aug. 12, 1980 to C. R. Bresson, discloses an asphaltic concrete composition comprising an asphalt, a mineral aggregate, and a radial teleblock diene/monovinyl aromatic copolymer having a weight ratio of diene to monovinyl aromatic monomer of at least about 75/25 to about 90/10 and a weight average molecular weight of from about 150,000 to about 300,000. The asphaltic concrete compositions disclosed in this patent are taught to exhibit excellent flexural fatigue test characteristics.
Similarly, U.S. Pat. No. 4,172,061, issued Oct. 23, 1979 to C. R. Bresson, discloses an asphaltic concrete composition comprising an asphalt, a mineral aggregate, and composition using a sufficient amount p a hydrogenated radial teleblock diene/monovinyl aromatic copolymer having a weight ratio of diene to monovinyl aromatic monomer of about 70/30 and a weight average molecular weight of from about 70,000 to about 150,000.
U.S. Pat. No. 4,585,816, issued Apr. 29, 1986 to J. F. Vitkuske et al., discloses a method of preparing a mixture of asphalt and a block copolymer of AB(BA).sub.n configuration, wherein n is an integer from 1 to 10, block A is a vinyl aromatic and block B is a diene.
U.S. Pat. No. 4,145,322, issued Mar. 30, 1979 to P. Maldonado et al., discloses a process for preparing a bitumen-polymer composition comprising 80 to 98% by weight of a bitumen having a penetration value between 30 and 220, 2 to 20% by weight of a block copolymer of styrene and a conjugated-diene having a molecular weight between 30,000 and 300,000, and 0.1 to 3% by weight of sulfur. The bitumen-polymer compositions of this patent are taught to have excellent mechanical properties even at low temperatures.
U.S. Pat. No. 3,440,195, issued Apr. 22, 1969 to G. W. Norcross, discloses a thermoplastic sealing composition comprising a product obtained by heating at a temperature between about 200.degree. F. (93.degree. C.) and about 400.degree. F. (204.degree. C.) for at least 6 hours a mixture of (1) from 3.0 to 5.5 parts by weight of an asphalt and (2) a block copolymer comprising from 12 to 20 percent by weight of a polystyrene homopolymer block and the remainder a block of a copolymer of styrene and butadiene, the total weight of styrene in the block copolymer being less than 30 percent.
Styrene/conjugated-diene block copolymers have also been used in combination with other types of polymers to prepare polymer-modified asphalt compositions. For example, U.S. Pat. No. 3,978,014, issued Aug. 31, 1976 to E. J. van Beem et al., discloses a bituminous composition comprising 75 to 92 weight percent of a bituminous component, 4 to 15 weight percent of a block copolymer of monoalkenyl aromatics and conjugated alkadienes, and 4 to 15 weight percent of a thermoplastic polymer having a molecular weight higher than 10,000, a solubility parameter between 7.8 and 8.8 and a crystallinity of less than 60 percent at 25.degree. C. The bituminous compositions disclosed in this patent are taught to have improved properties with regard to storage stability, penetration, softening point, breaking point and adhesion.
Similarly, U.S. Pat. No. 4,282,127, issued Aug. 4, 1981 to H. F. M. Desgouilles, discloses a bitumen-based composition containing a ternary mixture of 52 to 78 weight percent bitumen, 20 to 40 weight percent polyolefin, and 2 to 8 weight percent of a butadiene-styrene copolymer. The bitumen-based compositions disclosed in this patent are taught to be useful for sealing purposes.
More recently, epoxide-containing ethylene copolymers, such as glycidyl-containing ethylene copolymers, have been used to prepared polymer-modified asphalts. For example, PCT International Application WO 91/09907, published Jul. 11, 1991, discloses a thermoplastic polymer-linked-asphalt composition prepared by reacting asphalt with an epoxide-containing reactant polymer, preferably a glycidyl-containing ethylene copolymer. The polymer-linked-asphalt product disclosed in this application is taught to be particularly useful in road paving and roofing applications. This patent application additionally teaches on page 18, lines 11-30 that certain non-reactive diluent polymers may be added to the asphalt compositions disclosed therein.
Although various polymer-modified asphalt compositions are known in the art, there still exists a need in the asphalt industry for improved polymer-modified asphalt compositions. In part, this is due to the fact that new asphalt performance criteria or specifications are continually being developed by various state and federal agencies in an effort to increase the effective life of paved roads and other asphalt products under diverse climatic conditions. Not all existing polymer-modified asphalt compositions are able to meet these new, more stringent specifications. Accordingly, a need exists for improved polymer-modified asphalt compositions and methods for preparing such compositions.
It has now been discovered that polymer-modified asphalt compositions having excellent performance properties can be prepared using the novel combination of a glycidyl-containing ethylene copolymer and a styrene/conjugated-diene block copolymer. Moreover, this unique combination of copolymers has been found to be especially useful for adjusting the rheological properties of an asphalt to meet certain asphalt specification requirements.